idiot question-probably?

Be gentle with me, I have only been playing a few weeks,.
My question is:

On some hands, heads up, where both players call and show exactly the same hands eg. A,9 and A,9 (obviously diff suits) the pot is not always divided equally, it all goes so fast I often wonder what the hell is going on here, he gets 2000 chips i get 1200 out of a pot of 3200 chips,.

Im sure it s obvious but anyone tell me how it works please?

dont know never seen this? if its heads up should go evenly.

Unless you are shortstacked and he is full stacked.

like say you have 20k in chips and he has 30k and you both push in preflop. you can not win more then you put in the pot so you would take back your 20k and he would take the 30k back.

in your example of 3200 you most likely had only 12k at beginning of hand and he had you outchiped so he pushs and you call you can not split his extra 8k since you did not have him covered.

that woulds make sense, ive seen loads of weird splits now im looking for them, completely different hands getting unevenly split pots, guess ill have to observe more cloesly and get back here with some specific examples. thanks for your help.